Electromagnetic Interference (EMI) affects the electrical performance of various electronic devices, all the more, causes damages inside the electronic devices. Among the existing semiconductor packages, various EMI shielding structures have been proposed and built to isolate external EMI. However, the first priority to isolate external EMI is to have a good electrical connection to ground potential. Without appropriate grounding of EMI shielding structures, not only can external EMI not be isolated but also induce more serious EMI noise.
EMI shielding structures can be sorted into internal and external types where not one-single EMI shielding structure can fit for all packages, especially for leadframe-type semiconductor packages with signal leads and ground leads on the same side which will be more difficult to connect EMI shielding structures to the ground.
As revealed in U.S. Pat. No. 7,808,087, entitled “Leadframe IC packages having top and bottom integrated heat spreaders”, Zhao et al taught that an internal type EMI shielding structure consists of first and second caps inside a die-up or die-down package where the first and second caps define a die cavity. A leadframe includes a centrally located die attach pad, a plurality of leads, and a plurality of tie bars coupling to the die attach pad. An IC die is mounted to the die attach pad. Planar rim portions of the first and second caps that surround the cavity are coupled to the leadframe. The first and second caps and the leadframe form an enclosure structure that substantially encloses the IC die and shields EMI emanating from and radiating toward the IC die. The enclosed structure also dissipates heat generated by the IC die during operation. However, the revealed EMI shielding structure greatly interferes the formation of encapsulant where die sizes and leadframe layouts are quite limited.
As revealed in U.S. Pat. No. 5,294,826, entitled “Integrated circuit package and assembly thereof for thermal and EMI management”, Marcantonio et al taught that a heat spreader is disposed on the top surface of an encapsulant of a package as an EMI shielding structure where the heat spreader is called as a combined heat dissipating and EMI electromagnetic shielding structure. The die attach pad is electrically connected to the ground lead(s) through bonding wires where the heat spreader is attached to the bottom of the die attach pad so that the heat spreader is also electrically connected to the ground. However, this EMI shielding structure would encounter unbalanced mold flows between top and bottom molds when the encapsulant is formed where the leadframe design implemented for the leadframe-type package is quite limited. Moreover, when the die attach pad is too small or there is not enough wire bonding space for electrical connections between the die attach pad and ground leads within the limited molding space of a leadframe, the heat spreader loses its EMI shielding effect.